/* block.c -- block transfer
 *
 * Copyright (C) 2010--2012 Olaf Bergmann <bergmann@tzi.org>
 *
 * This file is part of the CoAP library libcoap. Please see
 * README for terms of use.
 */

#include "include/coap/config.h"

#if defined(HAVE_ASSERT_H) && !defined(assert)
# include <assert.h>
#endif

#ifdef WITH_ARDUINO
/* On Arduino the abort function, needed for assert, is defined in std lib */
#include <stdlib.h>
#endif

#include "include/coap/debug.h"
#include "include/coap/block.h"

#define min(a,b) ((a) < (b) ? (a) : (b))

#ifndef WITHOUT_BLOCK
unsigned int
coap_opt_block_num(const coap_opt_t *block_opt) {
    unsigned int num = 0;
    unsigned short len;

    len = coap_opt_length(block_opt);

    if (len == 0) {
        return 0;
    }

    if (len > 1) {
        num = coap_decode_var_bytes(COAP_OPT_VALUE(block_opt),
                                    COAP_OPT_LENGTH(block_opt) - 1);
    }

    return (num << 4) | ((*COAP_OPT_BLOCK_LAST(block_opt) & 0xF0) >> 4);
}

int
coap_get_block(coap_pdu_t *pdu, unsigned short type, coap_block_t *block) {
    coap_opt_iterator_t opt_iter;
    coap_opt_t *option;

    assert(block);
    memset(block, 0, sizeof(coap_block_t));

    if (pdu && (option = coap_check_option(pdu, type, &opt_iter)) != NULL) {
        block->szx = COAP_OPT_BLOCK_SZX(option);
        if (COAP_OPT_BLOCK_MORE(option))
            block->m = 1;
        block->num = coap_opt_block_num(option);
        return 1;
    }

    return 0;
}

int
coap_write_block_opt(coap_block_t *block, unsigned short type,
        coap_pdu_t *pdu, size_t data_length) {
    size_t start, want, avail;
    unsigned char buf[3];

    assert(pdu);

    /* Block2 */
    if (type != COAP_OPTION_BLOCK2) {
        warn("coap_write_block_opt: skipped unknown option\n");
        return -1;
    }

    start = block->num << (block->szx + 4);
    if (data_length <= start) {
        debug("illegal block requested\n");
        return -2;
    }

    avail = pdu->max_size - pdu->length - 4;
    want = 1 << (block->szx + 4);

    /* check if entire block fits in message */
    if (want <= avail) {
        block->m = want < data_length - start;
    } else {
        /* Sender has requested a block that is larger than the remaining
         * space in pdu. This is ok if the remaining data fits into the pdu
         * anyway. The block size needs to be adjusted only if there is more
         * data left that cannot be delivered in this message. */

        if (data_length - start <= avail) {

            /* it's the final block and everything fits in the message */
            block->m = 0;
        }
        else {
            unsigned char szx;

            /* we need to decrease the block size */
            if (avail < 16) { /* bad luck, this is the smallest block size */
                debug("not enough space, even the smallest block does not fit");
                return -3;
            }
            debug("decrease block size for %d to %d\n", avail, coap_fls(avail) - 5);
            szx = block->szx;
            block->szx = coap_fls(avail) - 5;
            block->m = 1;
            block->num <<= szx - block->szx;
        }
    }

    /* to re-encode the block option */
    coap_add_option(pdu, type,
            coap_encode_var_bytes(buf, ((block->num << 4) | (block->m << 3) | block->szx)), buf);

    return 1;
}

int
coap_add_block(coap_pdu_t *pdu, unsigned int len, const unsigned char *data,
        unsigned int block_num, unsigned char block_szx) {
    size_t start;
    start = block_num << (block_szx + 4);

    if (len <= start)
        return 0;

    return coap_add_data(pdu,
                         min(len - start, (unsigned int)(1 << (block_szx + 4))),
                         data + start);
}
#endif /* WITHOUT_BLOCK  */
